Certain emission control systems of modern internal combustion engine powered automotive vehicles use devices that rely upon vacuum power for their operation. Two examples of such devices are an exhaust gas recirculation (EGR) valve and a canister purge solenoid (CPS) valve. The usual source of vacuum for these devices is the intake manifold vacuum that is created in the engine's intake manifold when the engine is running.
At certain times during operation of an automotive vehicle, the magnitude, or intensity, of manifold vacuum may drop to rather low levels. Certain vacuum operated devices such as those mentioned above may require that the vacuum power to them be above a certain threshold level for them to operate in accordance with relevant specifications. The very low levels to which intake manifold vacuum may at times drop during operation of an automotive vehicle may be less than such threshold level. While such very low vacuum levels are typically only transitory in nature, they may contribute to transitory increases in emissions due to the inability of the emission control devices to receive at least the threshold level of vacuum. Because emission levels are strictly controlled by government laws and regulations, such transitory increases in emissions may result in non-compliance with relevant standards in some cases.
The present invention is directed to a vacuum boost valve that, when the intensity of vacuum from the vacuum source drops within a certain range immediately below the threshold level, is effective to maintain the vacuum input to such devices above the threshold level and thereby avoid situations such as those described above. A valve embodying principles of the invention may be used with various utilization devices other than the emission control devices that have been mentioned.
The invention will be described in detail with reference to accompanying drawings that illustrate a presently preferred embodiment of the invention according to the best mode contemplated at this time for carrying out the invention. Like reference numerals are used to designate like parts in the drawings.